Where is it forbidden? There were plenty of small businessmen in the bible. Are you saying that Josephs carpentry business would have been a sin if Joseph sold a small share of it in order to raise capital to buy some new tools? A share of stock is a share of a business.
Down through the ages people have citied the Bible as license for every action imaginable, you are no different, just don't fool yourself into thinking you are doing God's work.
Besides, greed is good, right?